1. Field of the Invention
The present invention relates generally to a position detecting arrangement and more specifically to an arrangement suitable for use in a fuel injection pump or the like.
2. Description of the Prior Art
In a previously proposed arrangement shown in FIGS. 1 and 2 of the drawings, a fuel injection pump (partially shown) includes a plunger 1 which is reciprocated by a cam disc 2 driven in synchronism with the crankshaft of an engine (not shown). The operation of the pump is such that during the induction stroke the plunger 1 is moved leftward (as seen in the drawings) permitting an axial groove 3 to register with a fuel inlet passage 4 whereby fuel is introduced into a variable volume chamber 5 defined between the plunger 1 and the bore in which the plunger is received. During the discharge stroke, the plunger is moved to reduce the volume of the variable volume chamber 5 compressing the fuel therein. Upon sufficient movement of the plunger into the bore, a radial bore 6 registers with an outlet passage 7 permitting the fuel compressed in the variable volume chamber to be discharged through an axial bore 8 to a fuel injector (not shown) via the outlet passage 7 and a check valve 9.
A discharge volume control valve 10 is slidably disposed about one end of the plunger 1 in a manner to control a drain passage 11 which fluidly communicates with the axial bore 8. The position of the valve 10 and therefore the amount of fuel permitted to be discharged via the drain passage 11, is controlled by a torque motor 12. A shaft 13 of the torque motor 12 is provided at one end therewith a crank or sectoral member which is connected to the valve 10 through a ball joint. With this arrangement, the rotation of the shaft 13 is translated into axial movement of the valve 10.
Energization of the torque motor 12 is controlled by a control arrangement including an accelerator pedal position responsive circuit 14, a engine revolution speed detector 15, a control circuit 16, an amplifier 17 and a feed-back control arrangement generally denoted by the numeral 18, connected as shown. The latter mentioned arrangement (18) includes an oscillator 19 and a position sensing device 20 including a shaft 21 movably under the influence of a cam 22 fixedly mounted on the afore-mentioned shaft 13. The shaft 21 is provided with a ferro-magnetic core 23 which is adapted to reciprocate backward and forth within induction coils 24 operatively connected to the oscillator 19.
However, this arrangement has suffered from the drawback that as the position of the valve member is sensed using an indirect inductance method, the above described apparatus has lacked the required degree of accuracy and thus induced poor injection quantity control due to insufficiently precise feedback control.